Field of the Invention
The present invention relates to digital adaptive voting for fault-tolerant digital systems.
The adaptive voting technique of the present invention uses dynamically gathered error data to differentiate good units from failing units in a redundant electronic system. Adaptive voting produces statistically more correct results than majority voting for redundant systems.
Adaptive voting is mathematically demonstrable to be a superior form of fault-tolerant voting for n units of an n-modular redundant system in the fact of widespread and frequent failures within multiple units of such a system. In other words, in the face of very serious performance degradations of multiple units of the system, adaptive voting may maintain system functionality even when all units of the system are suffering from intermittent faults. This is particularly advantageous for n-modular redundant Very Large Scale Integrated (VLSI) circuit technology.
A prior art treatise on adaptive voting is contained as Chapter IV, Adaptive Decision Elements in Failure-Tolerant Computer Design by William H. Pierce published by Academic Press, 1965. The adaptation procedures taught therein are entirely analog in nature. For example, the simplest adaption procedure is a procedure in which the error probability of the output of a circuit is inferred from conditions in the circuit, such as bias current. The quantity that indicates the error probability of the output of the circuit is used directly to set the vote-weight of the output in all later vote-takers. This is an open-loop adaption procedure, so it is stable and requires no special analysis. Other adaptation methods include linear-feedback circuits, linear low-pass filters and, as shown in pages 149-154 of the book entitled "The Theory and Practice of Reliable System Design", 1982, by Daniel P. Siewiorek and Robert S. Swarz, Digital Equipment Corporation, self-purging redundancy.